In our earlier work we found that the two to four cell developmental stages, in the oviducts of the hamster, produce a tetrapeptide of the structure: H-threonine-proline-arginine-lysine-OH. This compound, when injected into non-bred hamsters, prevents ovulations and consequently is classed as a contraceptive compound. The tetrapeptide appears to be attached to a large protein since we have partially isolated a protein with the same activity as the tetrapeptide and the original native tetrapeptide was non-dialyzable (suggesting large size). The tetrapeptide has been synthesized and is undergoing testing. In addition, since removal of the oviducts also prevents ovulation in non-bred hamsters, and a steroid produced by the oviductal stroma is increased following ovariectomy, we assume the steroid plays a role in maintaining normal cyclic ovarian activity. We assume the tetrapeptide causes a reduction in the level of steroid produced by the oviductal stroma. The attack on the problem will involve (1) isolation of the apparent protein carrier molecule, (2) determination of size of the protein molecule, (3) a demonstration that the tetrapeptide is, indeed, on the protein, (4) search for a similar protein in the developmental stages since the observed protein is in the plasma, (5) see if steroid terminates pregnancy, (6) prove oviduct is source tissue of the steroid, (7) continue assays of synthetic tetrapeptide on hamsters, mice and rats, and (8) test tripeptide, since compound works orally and tryptic digestion should have removed lysine.